Some estimates at the low end have placed the worldwide adult Bahá'í population at closer to 1.5 million and the adult Bahá'í population in India at 100,000 to 150,000.

Of the approximately 5 million members claimed world-wide by the Bahá'í authorities, nearly 2 million Bahá'ís are said to reside within the Republic of India.*

*These figures are based on official Bahá'í statistics. Since they only indicate the number of declarations (signed affirmations of belief in Bahá'u'lláh) and not active membership in a local Bahá'í community (regular attendance at functions, participation in the administrative process through voting etc.) the question of what they mean sociologically remains problematic. If the participatory qualification is required, then the numbers would fall off dramatically in both instances. Some estimates at the low end have placed the worldwide adult Bahá'í population at closer to 1.5 million and the adult Bahá'í population in India at 100,000 to 150,000.

(The Bahá'í Faith in India: A Developmental Stage Approach by William Garlington, published in Occasional Papers in Shaykhi, Babi and Bahá'í Studies, 2, 1997-06)

https://bahai-library.com/garlington_bahai_faith_india